1. Field of the Invention
The present invention relates to a mat member, a method for manufacturing the mat member, a muffler, and a method for manufacturing the muffler.
2. Discussion of the Background Art
Conventionally, it has been known that, in an internal combustion engine of an automobile or the like, noise is generated when exhaust gases, generated by the internal combustion engine, are discharged outside through an exhaust path.
Therefore, in order to reduce the noise, various mufflers to be installed in the exhaust path have been proposed.
In particular, in order to reduce noise in a high frequency range, a muffler including a mat member formed by inorganic fibers and the like, an inner pipe having a plurality of small holes around which the mat member is wrapped, and an outer pipe in which the mat member and the inner pipe are installed, has been used.
In a muffler of the above-mentioned kind, in general, exhaust gases discharged from an internal combustion engine are allowed to flow through the exhaust path into the inner pipe from the inlet side of the inner pipe. Then, the exhaust gases that have passed through the inner pipe are discharged outside from the outlet side of the inner pipe. At this time, noise in a high frequency range can be absorbed, diffused or otherwise treated by a plurality of small holes formed in the inner pipe and the mat member that surrounds these small holes. By forming the muffler in this kind of structure, it becomes possible to reduce, in particular, noise in a high frequency range.
A mat member that uses crystalline alumina fibers with its crystallinity controlled is disclosed as the mat member to be used for a muffler of the above-mentioned kind (JP-A 2006-022817).
The contents of JP-A 2006-022817 are incorporated herein by reference in their entirety.